Not sure if this applies to all stores or just QV Melbourne, but anything you buy from the 'Health and Beauty' section of BigW is non-refundable regardless of whether it is unopened, unused, even if the seal is visibly intact as it was in my case. The lady explicitly told me "no refunds or exchange on Health and Beauty for health and safety reasons" After a bit of cajoling (manager came) I was able to get a refund for a bottle of eucalyptus lotion I bought several days earlier (it was only four bucks and change but didn't wanna carry it around all day).
Health and Beauty doesn't appear under the product exclusion list on the BigW site and IIRC no signage advising people to choose carefully in that part of the store. Some years back I did return a hairdryer that I used twice but wasn't that good, so I guess I can sort of understand but if something is sealed even priceline will refund no issues.
Consumer Law trumps every rule stores make up. What is the reason that you are returning it, if it faulty or doesn't work as expected you are entitled to a refund